Waterfiends have a very high charm drop rate, especially for crimson charms (around 80%). At Ghorrock they drop 2 charms at a time but have a halved drop rate. For this reason, they are targeted by many players who wish to level up summoning quickly, making them more popular than other crimson charm droppers (demons, dust devils, etc.).

They are weakest against crossbow bolts, making any form of ranged a good choice for killing them. They can also be killed with higher level magic weapons, however they are immune to fire spells. Using darklight is a viable method for those wishing to use melee. The waterfiends at Ghorrock seem to be easier to hit, but also seem to deal more damage. At Ghorrock they are found on the lower floor after completing The Temple at Senntisten and are aggressive.

If the player is killing waterfiends for a Slayer assignment then they can gain 20% additional Slayer experience by equipping a demonic skull while killing waterfiends in the Wilderness. They can gain another 20% extra experience per kill while killing waterfiends in the Wilderness if they accept a special slayer contract from Erskine while assigned waterfiends as a Slayer task. These experience bonuses stack, meaning the player may gain 40% extra Slayer experience. Completing a special slayer contract rewards the player with a choice of coins or combat experience.

Waterfiends had an unannounced graphical update on 5 June 2008 - with this, some of their drops changed. Then, later that day, a system update after Smoking Kills was released to remove the drop change, only to be changed once again to fix some bugs and change some of the drops that were mentioned on the forums.